Intumescent materials contain ingredients that decompose on severe heating to generate gases and form an incombustible or low combustible residue. The expelled gases expand the residue to form a foam layer with improved thermal insulation properties. Materials also having a low heat release rate are advantageous in that once they are exposed to fire they release less heat to neighboring materials and diminish fire propagation. This is important because if, for example, a fire is started in a warehouse where large quantities of materials are stored, the fire will not get out of control and will be easily extinguished when fire retardant low heat release materials are used in place of ordinary polymers. Hence, major applications for low heat release polymers are for shipping pallets and shipping containers. However, such polymers can be used wherever there are fire safety concerns. The polymers can be used for automotive applications, such as for a fire shield for fuel tanks, car floors, bulk heads, wheel well covers or in other places in cars, trucks, boats, or airplanes to provide resistance to ignition or resistance to flame travel from the fire source to other areas. Applications in residential or commercial structures could help fire containment within each structure as well as slowing down the spread of fire from one structure to a neighboring structure. Hence, fire containment is more easily accomplished when flammable substrates are substituted with low heat release fire retardant polymers. Replacement of metal parts with such polymers, in applications requiring fire integrity, would also lead to appreciable weight reduction.
Shipping pallets will be used as an example to demonstrate the advantages of using polymers with low heat release rate, though the invention is not so limited. Pallets are portable platforms used for handling, storing or moving materials and heavy packages around in a warehouse or during shipping. Pallets have been traditionally made of wood. More and more plastics are being used to replace wood for the following benefits: (1) plastics maintain consistent weight and dimensions and are easy to stack; (2) plastics will not harbor bacteria and other contaminants; (3) plastics are easy to handle and clean; (4) plastics do not rot, splinter, or corrode; (5) plastics reduce transportation and disposal costs; (6) plastics are recyclable; (7) plastics perform consistently with automated equipment; (8) plastics are safe and easy to use; (9) plastics have improved toughness and stiffness; and (10) plastics lend themselves to embedding tracking devices.
As more plastic is being used in this market to replace wood pallets, fire performance becomes a concern. Plastic pallets are being required to meet or exceed the fire resistance standards for wood pallets. The standards include requirements that the material should have low heat release rate and low flame spread rate. By way of example, polyethylene, which is the preferred material for making pallets, melts, drips and burns at a relatively fast rate when exposed to fire. On the other hand, polyethylene is strong and durable, and has a low cost, high impact resistance and high chemical resistance. Thus, flame retardant systems have been developed for use with plastics, such as polyethylene, that attempt to provide intumescence, low heat release rate and low flame spread rate without decreasing the strength, durability, and impact and chemical resistance of the plastic to unacceptable levels. The same efforts have been made in other markets were flame retardant plastic materials are desirable. Invariably, however, some loss in the physical properties of the polymeric material is experienced upon addition of inorganic flame retardant materials to the polymer matrix.
The flame retardant materials must therefore provide a desired balance between physical properties, such as impact strength, tensile strength, elongation, and elasticity, and flame retardant properties, such as flame spread control, melt dripping, smoke, peak and average heat release rate, and total heat release. By way of example, U.S. Pat. No. 5,834,535 entitled “Moldable Intumescent Polyethylene and Chlorinated Polyethylene Compositions”, and U.S. Pat. No. 6,184,269 entitled “Moldable Intumescent Materials Containing Novel Silicone Elastomers” describe flame retardant plastic systems that address the need for achieving improved resistance to fire in desirable plastics without an unacceptable decrease in physical properties. However, the materials described therein contain a halogen material, namely, chlorinated polyethylene, which may generate corrosive HX gases, such as HCl. These toxic by-products are dangerous to persons exposed thereto. Many similar efforts to develop flame retardant systems utilize halogenated components because halogens are very efficient fire retardants. However, because they are environmentally unfriendly, it is desirable to find a fire retardant system that does not use halogens.
Thus, there is a need to formulate a non-halogen polymeric material that is strong and durable, that has a low cost, high impact resistance and high chemical resistance, that burns at a slow rate, that does not melt, drip and flow, and that releases a relatively low amount of heat when exposed to fire.